Test Helpers

One of the major issues in testing web applications is that all code is
event-driven and therefore has the potential to be asynchronous (i.e. output can
happen out of sequence from input). This has the ramification that code can be
executed in any order.

An example may help here: Let's say a user clicks two buttons, one after another
and both load data from different servers. They take different times to respond.

When writing your tests, you need to be keenly aware of the fact that you cannot
be sure that the response will return immediately after you make your requests,
therefore your assertion code (the "tester") needs to wait for the thing being
tested (the "testee") to be in a synchronized state. In the example above, that
would be when both servers have responded and the test code can go about its
business checking the data (whether it is mock data, or real data).

This is why all Ember's test helpers are wrapped in code that ensures Ember is
back in a synchronized state when it makes its assertions. It saves you from
having to wrap everything in code that does that, and it makes it easier to read
your tests because there's less boilerplate in them.

Ember includes several helpers to facilitate acceptance testing. There are two
types of helpers: asynchronous and synchronous.

Asynchronous Helpers

Asynchronous helpers are "aware" of (and wait for) asynchronous behavior within
your application, making it much easier to write deterministic tests.

Also, these helpers register themselves in the order that you call them and will
be run in a chain; each one is only called after the previous one finishes. You can rest assured, therefore, that the order you call them in will also
be their execution order, and that the previous helper has finished before the
next one starts.

Fills in the selected input with the given value and returns a promise that
fulfills when all resulting async behavior is complete. Works with <select> elements as well as <input> elements. Keep in mind that with <select> elements, value must be set to the value of the <option> tag, rather than its content (for example, true rather than "Yes").

Finds an element within the app's root element and within the context
(optional). Scoping to the root element is especially useful to avoid
conflicts with the test framework's reporter, and this is done by default
if the context is not specified.

Wait Helpers

The andThen helper will wait for all preceding asynchronous helpers to
complete prior to progressing forward. Let's take a look at the following
example.

First we visit the new posts URL "/posts/new", enter the text "My new post"
into an input control with the CSS class "title", and click on a button whose
class is "submit".

We then make a call to the andThen helper which will wait for the preceding
asynchronous test helpers to complete (specifically, andThen will only be
called after the new posts URL was visited, the text filled in and the
submit button was clicked, and the browser has returned from doing whatever
those actions required). Note andThen has a single argument of the function
that contains the code to execute after the other test helpers have finished.

In the andThen helper, we finally make our call to assert.equal which makes an
assertion that the text found in the first li of the ul whose class is "posts"
is equal to "My new post".

Custom Test Helpers

For creating your own test helper, run ember generate test-helper
<helper-name>. Here is the result of running ember g test-helper
shouldHaveElementWithCount:

Ember.Test.registerAsyncHelper and Ember.Test.registerHelper
are used to register test helpers that will be injected when startApp is
called. The difference between Ember.Test.registerHelper and
Ember.Test.registerAsyncHelper is that the latter will not run until any
previous async helper has completed and any subsequent async helper will wait
for it to finish before running.

The helper method will always be called with the current Application as the
first parameter. Other parameters, such as assert, need to be provided when calling the helper. Helpers need to be registered prior to calling
startApp, but Ember CLI will take care of it for you.

Finally, don't forget to add your helpers in tests/.eslintrc.js and in
tests/helpers/start-app.js. In tests/.eslintrc.js you need to add it in the
globals section, otherwise you will get failing ESLint tests: